Rolling Die Nitrided Surface Uniformity to Prevent Tooth Chipping
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Solution Overview
Problem
The nitride layer on the molded surface of rolling dies tends to be deeper at the crests of the working teeth and shallower at the roots, leading to uneven durability and potential chipping.
Innovation Solution
A rolling die with a nitride layer extending 20 to 70 µm from the molded surface, a surface hardness of at least 1100 HV, and a controlled depth change rate from crests to roots of no more than 30%, combined with compressive residual stress and an oxide film made of Fe3O4, to enhance durability and prevent chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ion nitriding is performed on the molded surface, then the molded surface is hardened and wear resistance is improved, but the nitride layer depth becomes uneven between crests and roots of working teeth
Solution Approach 1:
The patent applies local quality by performing shot peening specifically on portions of the molded surface where the nitride layer depth is excessive (primarily the crests of working teeth). This localized treatment reduces the nitride layer depth in specific areas to achieve uniformity across the entire molded surface, while preserving the hard nitride layer in areas where it is needed for wear resistance.
Solution Approach 2:
The patent employs a two-stage process where ion nitriding is performed first to harden the surface, followed by shot peening to remove excess nitride layer. This sequential approach allows the process to rush through the nitriding phase to achieve hardness, then quickly correct the depth uniformity issue through selective material removal.
2Duration of action of stationary object
If the nitride layer is made deeper to increase durability, then wear resistance improves, but the molded surface becomes more prone to chipping
Solution Approach 1:
The patent applies local quality by selectively reducing nitride layer depth at the crests of working teeth through shot peening, while maintaining adequate nitride layer depth at the roots. This creates a gradient structure where the roots retain deep nitride layers for wear resistance, while the crests have reduced depth to prevent chipping, optimizing both durability and toughness locally.
Solution Approach 2:
The patent changes the nitride layer depth parameter spatially across the molded surface. By controlling the shot peening process, the nitride layer depth is reduced in specific regions (crests) while maintaining or achieving uniformity in other regions (roots), thereby optimizing the balance between wear resistance and chipping resistance through parameter variation.
3Manufacturing precision
If shot peening is performed to reduce nitride layer depth, then uniformity improves, but the surface roughness increases
Solution Approach 1:
The patent optimizes shot peening parameters (shot size, projection pressure, projection time) to achieve the desired nitride layer depth reduction while minimizing surface roughness increase. By carefully controlling these parameters, the process removes excess nitride layer material uniformly without creating excessive surface irregularities, balancing depth uniformity with surface finish quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures uniform nitride layer depth, increased abrasion resistance, and improved toughness of the molded surface, thereby enhancing the durability of the rolling die.
Implementation Method 1
The tool base material includes a nitride layer in which nitrogen is diffused
Implementation Method 2
an oxide film is formed on a portion of the nitride layer (15) that is positioned 0.5 to 5 μm deep from the molded surface, the oxide film being mainly made of Fe 3 O 4 that is obtained by oxidizing the tool base material
Data Source
Figure 1(a)~1(b)
Figure 2
AI summary
Provided is a rolling die that increases the durability of a nitrided molded surface. The rolling die (1) includes a tool base material that is made of steel and has a molded surface (2) on which a plurality of working teeth (10) is formed. The tool base material includes a nitride layer (15) in which nitrogen is diffused. The nitride layer (15) is disposed to reach a position that is 20 to 70 µm in depth from the molded surface (2). The molded surface (2) has a surface hardness of at least 1100 HV. The rate of depth change from the depth (D1) of the nitride layer (15) at crests (11) of the working teeth (10) to the depth (D2) of the nitride layer (15) at roots (13) of the working teeth (10) is not higher than 30%.